A. Features of Atoms in the Periodic Table Atomic Radius Difficult to measure, since atoms have electron. down a group across a period

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1 [3.2A Periodicity: Trends in the Periodic Table] pg. 1 of 5 Curriculum: Vertical and horizontal trends in the periodic table exist for atomic radius, ionic radius, ionization energy, electron affinity and electronegativity. A. Features of Atoms in the Periodic Table Atomic Radius Difficult to measure, since atoms have electron without a Measured as point between nuclei of 2 identical atoms: Van de Waals radius Covalent/Metallic bond radius Ionic Radius Ionization Energy Electron Affinity Electronegativity Metallic Character Radius of an atom s Measured as distance between anion and cation in a crystal lattice Vary according to of ion Energy required to remove 1 mole of electrons from 1 mole gaseous atoms to produce 1 mol of gaseous ions, each with a charge of 1+ Equation: o IE = the energy input for this to happen to 1 mole of atoms IE = tendency for atom to lose electron Energy released when 1 mole gaseous atoms each acquires an electron to form 1 mole of gaseous 1- ions Equation: o EA = the energy per mole when the above equation happens EA = tendency for atom to gain e - How much power an atom has on another atom s electrons Derived from IE and EA Relative Scale, ( ) to ( ), no units o ( ), most electronegative o and ( ), least electronegative Does not describe physical properties like luster, ductility, conductivity Does describe how likely an atom is to electrons and become the ion in an bond o This is a property B. Summary of Trends 1 1 By Itub - Own work, CC BY-SA 3.0,

2 [3.2A Periodicity: Trends in the Periodic Table] pg. 2 of 5 C. Understanding Periodic Trends Periodic trends are determined by the between the and, especially the electrons A formula that relates the strength of attraction between charged particles is Coulomb s law: F = k q 1q 2 r 2 2 F = force of k = q 1 = first q 2 = second r = between charges Interactions between charges in an atom: 1) are attracted to the nucleus 2) Electron Electron undo some of the attraction of electrons to the nucleus Effective nuclear charge o Portion of charge felt by an electron o Charge felt by an individual valence electron is important o The nuclear charge felt by valence electrons is lessened mostly by repulsions from electrons o Electrons sharing a valence shell slightly repel each other Z R inner - R val nuclear charge Z = nuclear charge # valence electrons below vse - 0.5(# other valence electrons) Modified Coulomb s law o We aren t interested in calculating the values for things like ionization energy or electron affinity o We want to the attraction of valence electrons to the nucleus o To do this, we will Coulomb s law o This formula is only an of the original, and only gives relative values that help explain patterns in the periodic table F = (Z eff)(1 ) n 2 Where effective nuclear charge 1- = charge on the electron n = number of energy levels Practice: Hydrogen and Helium Atomic #1 Z = R valence = e = n = F = Atomic #1 Z = R valence = e = n = F = The electrons are attracted to the nucleus in Comparison: Helium has a force of between each valence electrons and nucleus. Hydrogen feels a force of This means helium will have a atomic radius and higher Metallic character will be in because it is less willing to lose an electron, due to the attraction between its nucleus and electrons 2 By Nein Arimasen - Own work, CC BY-SA 3.0,

3 [3.2A Periodicity: Trends in the Periodic Table] pg. 3 of 5 D. Periodic Trends Based on Coulomb s Law Hydrogen Z R inner - R val Helium n 2 n=2 1s 2 2s 1 1s 2 2s 2 1s 2 2s 2 2p 1 1s 2 2s 2 2p 2 1s 2 2s 2 2p 3 1s 2 2s 2 2p 4 1s 2 2s 2 2p 5 1s 2 2s 2 2p 6 F = (Z eff)(1 ) Force/e- n=3 [Ne]3s 1 [Ne]3s 2 [Ne]3s 2 3p 1 [Ne]3s 2 3p 2 [Ne]3s 2 3p 3 [Ne]3s 2 3p 4 [Ne]3s 2 3p 5 [Ne]3s 2 3p 6 Coulombic Force AR IE EA EN MC Trend across a period Force attracting vse-, greater Zeff going across the period due to consistent n-value Increased attraction causes vse- to be brought closer to the nucleus, AR Strong attraction causes nucleus to hold tightly to vse-. IE Nuclear, AR becomes. Incoming e- get closer to nucleus, feel greater force of attraction, which releases more energy when the electron binds to the atom. EA Smaller atoms across a period, positive nucleus closer to vse- of other atoms, easier to attract those e-. EN Going across a period, Coulombic attraction increases, and elements are less likely to lose valence electrons in a chemical reaction. MC Trend down a group Force attracting vse-, due to increasing distance of valence shell Decreased attraction causes vse- to be further out, AR Weak Coulombic attraction, outer e- not firmly held, IE to remove electron Less coulombic attraction, due to more shells, distance and electron repulsion. Incoming electron cannot get as close to nucleus, so less energy is released. EA Larger atoms, positive nucleus if further from e- of nearby atoms, harder to attract e-. EN As atomic radius increases down a group, and coulombic attraction decreases, valence electrons are loosely held and it is easier for them to be lost in a chemical reaction. MC

4 [3.2A Periodicity: Trends in the Periodic Table] pg. 4 of 5 E. Periodic Trends: Ionic Radius 1) How does the radius change when an atom becomes an ion? n=3 Sodium Atom Sodium Ion S 2- Magnesium Atom Magnesium Ion Mg 2+ Aluminum Atom Aluminum Ion Al 3+ Radius 154 pm 116 pm 130 pm 86 pm 118 pm 68 pm Losing electrons makes a positive ion smaller than the atom it came from This is because an entire energy level is and because the Coulombic force is higher for an ion o.the ion is because the electrons are in more. Comparing positive ions in the same period, the Coulombic attraction increases as the nuclear charge increases. Positive ions decrease in size ( gets smaller) moving left to right across a period Sulfur atom Sulfur Ion Chlorine atom Chlorine Ion n=3 radius Adding electrons makes a negative ion than the atom it came from The electrons that get added to the valence shell electron This the Coulombic force holding the electrons to the nucleus The electrons go a little farther out and the resulting ion is Comparing the negative ions, the size of negative ions down a period 2) Decreasing ion size down a period Both positive and negative ions in radius down a group Going down a group the distance between the nucleus and outer electrons, even in an. This decreases Coulombic attraction and the outer electrons can move away more.

5 [3.2A Periodicity: Trends in the Periodic Table] pg. 5 of 5 E. Explaining Metallic Behavior Curriculum: Trends in metallic and non-metallic behaviour are due to the trends above. 1) Metallic Character Revisited Metallic character is a type of reactivity, so it is a property: o Tendency to valence electrons in a chemical reaction and become the in an ionic bond o Metals are (don t like electrons), non-metals are (like electrons) Several periodic properties contribute to the metallic character of an element: Atomic Radius left to right are on the left, so they have a atomic radius Valence electrons are from the nucleus, so are held tightly and can come off more easily Ionization Energy The ionization energy is for metals energy is needed to pull an electron off Easier for the formation of Electronegativity This is the pull that an atom has on the of another atom Smaller atoms the positive pull of their nucleus more, which electrons Metals have atoms, so the of their nuclei is not as pronounced